The present invention relates to an air cleaner for an internal combustion engine.
Conventionally, an air cleaner for a vehicle-mounted internal combustion engine has a first housing having an inlet and an opening, a second housing having an outlet and an opening, a filter element arranged between the opening of the first housing and the opening of the second housing.
The wall portion of the housing of the air cleaner described in Japanese Laid-Open Patent Publication No. 2002-21660 is formed by sound absorbing material composed of filter paper, nonwoven fabric, or porous material such as open-cell sponge. The inner wall surface of the housing of the air cleaner described in Japanese Laid-Open Utility Model Publication No. 64-11359 is constituted by a sound absorbing layer such as foamed polyurethane. In these air cleaner, the sound absorbing material reduces intake noise.
The present inventors discovered that, in an air cleaner, the sound pressure levels of components of a low frequency range of intake noise are greater than the sound pressure levels of components of a high frequency range, and that the low frequency components are the main cause of the noise. However, conventional air cleaners having the above described sound absorbing material or sound absorbing layer cannot readily reduce the low frequency components.